A fuel cell is typically formed in a stack structure where a plurality of unit cells are stacked one upon another. In use, heat is generated in the fuel cell. In order to cool the fuel cell, a cooling plate having a coolant passage is inserted every several unit cells. Coolant is circulated in the cooling plates through the coolant passages and cools the fuel cell.
If the electrical conductivity of the coolant is high, electricity generated in the fuel cell tends to partially leak into the coolant, resulting in waste of electricity and reduction of power. Therefore, pure water which is low in electric conductivity and thus highly insulative is typically used as fuel cell coolant.
However, when used in a vehicle fuel cell or a household cogeneration system, such fuel cell coolant will be cooled to the atmospheric temperature when the cell or the system is out of use and may be frozen at a temperature below zero, seriously damaging its cooling plates due to volumetric expansion of the coolant and greatly deteriorating the function of the fuel cell.
In order to prevent such freezing, glycol or alcohol may be blended in coolant as a base component. A fuel cell coolant comprised of water and glycol as a base component and an amine based alkaline additive has been proposed (Japanese Unexamined Patent Publication 2001-164244).